1. Field of the Invention
This invention is directed to a method or apparatus for making engineering changes to circuit modules. While the invention can be used to change circuit connections, the invention is particularly directed to adding discrete circuit elements or devices to circuit modules and thereby changing or adding to the electrical functions performed by the circuit module.
After multi-chip circuit carrier modules are in production, the time required to redesign and put in production a new version of the module is weeks or even months. Typically design faults in a module are corrected by adding and/or deleting electrical connections between chips on the carrier substrate of the module or electrical connections on the printed circuit board on which the module is mounted. However, the design itself may change such that new functions or enhancements of functions are added. Often in this event, discrete circuit components or chips must be added to the module
In high density circuit packaging, the multi-chip carrier modules and the printed circuit boards or cards on which they are mounted are designed for optimum use of the surface area (or real estate) of the card. To add additional discrete circuit elements to make an engineering change to a module on the card may not be possible simply because there is not sufficient remaining surface area on the card.
2. Description of Prior Art
There are numerous examples in the art of printed circuit cards and integrated circuit modules wherein engineering changes are accomplished with wiring changes or interconnection line changes. In some cases the interconnection changes are accomplished with jumper wires or fly wires. In others the interconnection lines are changed by attaching an auxiliary printed circuit board or card. In yet other inventions, the wiring changes ar accomplished in multilayer substrates where the new interconnection lines may be buried; i.e. in an internal layer in a multilayer substrate.
All of the above examples use new real estate or surface area on the card if they add additional electrical components. One such example is U.S. Pat. No. 4,731,704 issued to A. Lochner. In the Lochner patent additional components are attached to the main or original printed circuit board. New electrical connections for the added components are provided by a new printed circuit foil which is attached to component pins protruding through the original printed circuit board. While Lochner teaches a technique for adding functional component engineering changes to a module, the invention presumes there is surface area available on the original board for the addition of new components.